Irradiation Effects on Titanium Dioxide Electrodes for Lithium Ion Batteries

This dissertation presents the mechanisms of irradiation induced defects and the resulting electrochemical response of TiO2 anode for ­lithium-ion-batteries. The objective is to realize pathways by which irradiation could be used to enhance the energy density of rechargeable lithium ion batteries in order to provide power to applications under extreme environments. Recent studies suggest that the presence of structural defects (e.g. vacancies and interstitials) in metal oxides may enhance the electrochemical charge storage capacity in electrode materials. One approach to induce defect formation in electrode materials is to use ion irradiation, which has been proven to produce point defects in a target material. The effect of low energy proton irradiation, at both room temperature and 250˚C, on amorphous and anatase TiO2 nanotube electrodes, as well as heavy-ion irradiation on single crystal TiO2 is discussed. Nanotube electrodes, as well as lamella prepared from single crystal samples, were characterized with Raman spectroscopy and transmission electron microscopy to evaluate the structural phenomena that occur during irradiation. Furthermore, various electrochemical tests have been performed to study the irradiation response to lithiation after irradiation. It has been shown in this work that tailoring the defect density in metal oxides through ion irradiation presents new avenues for design of advanced electrode materials

Effects of Proton Irradiation on Structural and Electrochemical Charge Storage Properties of TiO\u3csub\u3e2 \u3c/sub\u3eNanotube Electrode for Lithium-Ion Batteries

The effects of proton irradiation on nanostructured metal oxides have been investigated. Recent studies suggest that the presence of structural defects (e.g. vacancies and interstitials) in metal oxides may enhance the material’s electrochemical charge storage capacity. A new approach to introduce defects in electrode materials is to use ion irradiation as it can produce a supersaturation of point defects in the target material. In this work we report the effect of low-energy proton irradiation on amorphous TiO2 nanotube electrodes at both room temperature and high temperature (250 ˚C). Upon room temperature irradiation the nanotubes demonstrate an irradiation-induced phase transformation to a mixture of amorphous, anatase, and rutile domains while showing a 35% reduction in capacity compared to anatase TiO2. On the other hand, the high temperature proton irradiation induced a disordered rutile phase within the nanotubes as characterized by Raman spectroscopy and transmission electron microscopy, which displays an improved capacity by 20% at ~ 240 mAh g-1 as well as improved rate capability compared to unirradiated anatase sample. Voltammetric sweep data was used to determine the contributions from diffusion-limited intercalation and capacitive processes and it was found that the electrodes after irradiation has more contributions from diffusion in lithium charge storage. Our work suggests that tailoring the defect generation through ion irradiation within metal oxide electrodes could present a new avenue for design of advanced electrode materials

Amorphous Boron Nanorod as an Anode Material for Lithium-Ion Batteries at Room Temperature

We report an amorphous boron nanorod anode material for lithium-ion batteries prepared through smelting non-toxic boron oxide in liquid lithium. Boron in theory can provide capacity as high as 3099 mAh g-1 by alloying with Li to form B4Li5. However, experimental studies of boron anode were rarely reported for room temperature lithium-ion batteries. Among the reported studies the electrochemical activity and cycling performance of bulk crystalline boron anode material are poor at room temperature. In this work, we utilized amorphous nanostructured one-dimensional (1D) boron material aiming at improving the electrochemical reactivity between boron and lithium ions at room temperature. The amorphous boron nanorod anode exhibited, at room temperature, a reversible capacity of 170 mAh g-1 at a current rate of 10 mA g-1 between 0.01 and 2 V. The anode also demonstrated good rate capability and cycling stability. Lithium storage mechanism was investigated by both sweep voltammetry measurements and galvanostatic intermittent titration technique (GITT). The sweep voltammetric analysis suggested that the contributions from lithium ions diffusion into boron as well as the capacitive process to the overall lithium charge storage are 57% and 43%, respectively. Results from GITT indicated that the discharge capacity at higher potentials (\u3e ~ 0.2 V vs, Li/Li+) could be ascribed to a capacitive process and at lower potentials (\u3c ~0.2 V vs, Li/Li+) to diffusion-controlled alloying reactions. Solid state nuclear magnetic resonance (NMR) measurement further confirmed that the capacity is from electrochemical reactions between lithium ions and the amorphous boron nanorod. This work provides new insights into designing nanostructured boron material for lithium-ion batteries

Electrochemically Induced Amorphous-to-Rock-Salt Phase Transformation in Niobium Oxide Electrode for Li-Ion Batteries

Intercalation-type metal oxides are promising negative electrode materials for safe rechargeable lithium-ion batteries due to the reduced risk of Li plating at low voltages. Nevertheless, their lower energy and power density along with cycling instability remain bottlenecks for their implementation, especially for fast-charging applications. Here, we report a nanostructured rock-salt Nb2O5 electrode formed through an amorphous-to-crystalline transformation during repeated electrochemical cycling with Li+. This electrode can reversibly cycle three lithiums per Nb2O5, corresponding to a capacity of 269 mAh g−1 at 20 mA g−1, and retains a capacity of 191 mAh g−1 at a high rate of 1 A g−1. It exhibits superb cycling stability with a capacity of 225 mAh g−1 at 200 mA g−1 for 400 cycles, and a Coulombic efficiency of 99.93%. We attribute the enhanced performance to the cubic rock-salt framework, which promotes low-energy migration paths. Our work suggests that inducing crystallization of amorphous nanomaterials through electrochemical cycling is a promising avenue for creating unconventional high-performance metal oxide electrode materials

The Synthesis of Titanium (IV) Oxide Nanotubes via Hydrothermal Process for use as Anode Material in Sodium-ion Batteries

Rechargeable lithium-ion batteries (LIBs) have been commercialized because they are an efficient energy storage device for many applications. We must reevaluate LIBs to develop sustainable energy in the future. Sodium-ion batteries (NIBs) are being considered as a replacement for LIBs due to the high availability and low cost of sodium, and their standard electrode potential allowing them to provide comparable specific capacity. Synthesizing an anode material for use in a NIB with a comparable cell potential and capacity is the focus of current research. Titania is a promising anode material due to its excellent cyclic stability, reversible sodium intercalation, and high rate performance. Herein, hydrothermal synthesis was utilized to form titania nanoparticles for use as an anode material. The structures were analyzed and characterized using SEM and TEM to confirm morphology and size distribution, while XRD determined the phase of the titania. The parameters of temperature, concentration of NaOH, and duration of hydrothermal synthesis were manipulated to optimize the titania structures. The resulting materials were used as the anode in a NIB and the cyclic performance was tested

Hydrothermal Synthesis of Titanate Nano-Structures for use as Anode Material in Sodium-Ion Batteries

Lithium-ion batteries (LIBs) have been successful in a wide variety of applications from cell phones to electric cars, but concerns about scarcity and the price of lithium are steering research toward alternative materials for rechargeable batteries. Due to the abundance of sodium and its chemical and electrochemical similarities to lithium, sodium-ion batteries (NIBs) present one likely alternative to LIBs. Some challenges remain in the development of NIBs, especially in the development of suitable anode materials. As a highly stable, inexpensive, nontoxic, and abundant material, titania has gained attention for energy storage applications. This work studies titanate nano-structures created through hydrothermal treatment. Morphology, crystallinity, and electrochemical performance are analyzed as a function of treatment temperature and molarity. Samples are characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the electrochemical performance is determined by cycling coin-type half-cells

Examining the Effects of Phosphazene Additives in Electrolytes for Sodium Ion Batteries

Lithium ion batteries (LIBs) currently dominate the battery market due to their high capacity and cycling stability. However, because of lithium’s scarcity, the forthcoming demand for large scale energy storage will need to be satisfied by systems that use more abundant resources. Sodium ion batteries (NIBs) are a suitable alternative, but for NIBs to compete with LIBs their cycle life and capacity need to be improved. One way of improving these characteristics is to alter the electrolyte. In this study, the effect of the phosphazene additive FM2 was examined by varying the additive percentage in relation to carbonate solvent in a NIB system. The efficiency, lifespan, and specific capacity of cells with the FM2 additive were compared to cells made with the commercially used fluoroethylene carbonate (FEC) additive. The results of this study will add to the ongoing effort to develop more sustainable battery systems. This work is supported by the National Science Foundation via the Research Experience for Undergraduates Site: Materials for Society at Boise State University (DMR 1658076)

Trends in Na-Ion Solvation with Alkyl-Carbonate Electrolytes for Sodium-Ion Batteries: Insights from First-Principles Calculations

Classical molecular dynamics (MD) simulations and M06-2X hybrid density functional theory calculations have been performed to investigate the interaction of various nonaqueous organic electrolytes with Na+ ion in rechargeable Na-ion batteries. We evaluate trends in solvation behavior of seven common electrolytes namely pure carbonate solvents (ethylene carbonate (EC), vinylene carbonate (VC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC)) and four binary mixtures of carbonates (EC:PC, EC:DMC, EC:EMC, and EC:DEC). Thermochemistry calculations for the interaction of pure and binary mixtures of carbonate solvents with Na+ ion, Na+ ion coordinated with carbonate clusters obtained from molecular dynamics simulations, show that the formation of Na-carbonate complexes is exothermic and proceeds favorably. Based on the highest binding energy (ΔEb), enthalpy of solvation (ΔH(sol)), and Gibbs free energy of solvation (ΔG(sol)) values for the interaction of Na+ ion with carbonate solvents, our results conclusively show that pure EC and binary mixture of (EC:PC) are the best electrolytes for sodium-ion based batteries. Quantum chemical analyses are performed to understand the observed trends in ion solvation. Quantum theory of atoms in molecules (QTAIM) analysis shows that the interactions in Na-carbonate complexes are classified as a closed-shell (electrostatic) interaction. The localized molecular orbital energy decomposition analysis (LMO-EDA) also indicates that the electrostatic term (ΔEele) in the interaction energy between Na+ ion and carbonate solvents has the highest value and confirms the results of QTAIM about the electrostatic nature of Na+ ion interaction. The noncovalent interaction (NCI) plots indicate that the noncovalent interactions responsible for the formation of Na-carbonate complexes are strong to weak attractive interactions. Density of state (DOS) calculations show that the HOMO−LUMO energy gap in the EC, VC, PC, BC, DMC, EMC, and DEC increases as they interact with Na+ ion, although the HOMO−LUMO energy gap decreases with the addition of EC as an electrolyte additive to PC, DMC, and EMC. Calculated trends based on these quantum chemical calculations suggest that EC and binary mixture of EC:PC emerge as the best electrolytes in sodium-ion batteries, which is in excellent agreement with previously reported in silico experimental results

Oxide-Coated Titanium Dioxide Nanotube Anodes in Sodium-Ion Batteries

Although lithium-ion batteries are commonly used for energy storage, the cost and availability of source materials have accelerated research in alternative sodium-ion batteries (NIBs). However, the energy storage capacity and cycle life of NIBs must be increased before becoming commercially viable. One approach to improving NIB performance is to stabilize the solid electrolyte interphase (SEI). The SEI develops when the electrolyte and electrodes react, forming an additional layer through which ions must diffuse. An unstable SEI layer can cause irreversible capacity loss, but an artificial SEI layer may lower capacity loss and increase stability over many cycles. Coating the anode surface with thin layers of different materials has been shown to stabilize the SEI. This work studies the effect of coating anatase and amorphous titanium dioxide nanotube anodes with thin films of aluminum oxide and additional titanium dioxide via atomic layer deposition (ALD). The capacity, cycle life, and role of surface energy will be investigated as a function of the thickness of these oxide coatings

​ An investigation into the Degradation of Sodium Ion Electrolytes and their Effects on Battery Performance

Current battery research is dominated by lithium-ion technology, but the lithium based cell is neither sustainable nor environmentally responsible. A potential solution for future battery development is the chemically analogous sodium-ion cell. Although most research in this area has focused on the electrode materials, the electrolyte serves a critical—yet understudied—purpose in the sodium-ion battery. This research is aimed at understanding the electrochemical behavior of the sodium electrolyte in search of building a better battery. An electrolyte consisting of a sodium hexafluorophosphate (NaPF6) salt and different mixtures of solvents (cyclic and acyclic carbonates) was utilized as a base study of degradation. Various additives were utilized to hinder the degradation of the electrolyte to improve the performance and safety of the cells. Using fluoroethylene carbonate (FEC) to stabilize the solid electrolyte interface and triethoxy trifluoroethoxy phosphazene (FM2) to remove damaging hydrofluoric acid, nuclear magnetic resonance (NMR) and electrochemical cycling show here the impact on performance of the additives in multiple metrics